1. Field of the Invention
This invention relates to a piezoelectric ceramic that has various applications such as ceramic filter, piezoelectric buzzer, piezoelectric ignition, ultrasonic vibrator, etc. and its production method.
2. Description of the Prior Art
Such piezoelectric ceramics as two-component system of Pb(Ti, Zr)O.sub.3, three component system of Pb(Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3, four-component system of Pb(Zn.sub.1/3 Nb.sub.2/3).sub.w (Sn.sub.1/3 Nb2/3).sub.x Ti.sub.y Zr.sub.z O.sub.3 and the like have been so far known. The structure of these conventional piezoelectric ceramics shows a uniform single composition throughout its entirety and any part of the ceramics shows the identical composition within certain tolerance and also has the identical piezoelectric characteristics. Therefore, when a piezoelectric ceramic for a certain specific application is to be selected the one with a composition that shows piezoelectric characteristics closest to requirements is selected or some improvements are applied to the composition to satisfy the requirements in piezoelectric characteristics.
However, there is a limit to satisfying the required piezoelectric characteristics by resorting only to selection from the compositions available as in the foregoing or improvement of such existing compositions. Especially, it is difficult to obtain a piezoelectric ceramic that shows small changes in piezoelectric characteristics like resonant frequency, etc. by temperature and time.